Fruit graders usually comprise an endless circuit of carriers or "cups" on a conveyor chain with the cups situated to unload fruit at stations appropriate to, for example, fruit weight, size, colour or defect type. There are currently two predominant methods of sizing fruit, being weighing and imaging (using a video image to gain information about the fruit). The weighing method requires that the fruit are separated, that is one per cup and that the cup be stable with minimum external forces. The imaging method requires that fruit be rotated between large diameter rollers in order that multiple views may be obtained (especially for non-spherically shaped fruit). Many different designs of cup and their actuating systems are known to the prior art.
One type of cup system has been termed a "back-tipping" cup. An example of this cup type is disclosed in U.S. Pat. No 4,403,669 issued to Raz. A back tipping-cup has an actuating mechanism which allows the fruit in the cup to be dropped backwards, away from the direction the fruit is travelling. This type of system requires that the cup be tipped from horizontal down to almost vertical in order that the produce may be dropped out of the cup. This system also requires a large cup in order that the fruit may fall unimpeded through the gap left by the tipped cup and therefore fewer cups per unit length of conveyor and lower through-put of produce results. The back-tipping method also requires that the produce be dropped from a greater height when compared to some other devices so that the large cup may be swung almost to vertical, increasing damage to the produce.
Another prior art cup system involves side-tipping cups which have a "kicker" or "ejector" incorporated on one side of the cup. An example is disclosed in U.S. Pat. No 5,029,692 to Warkentin. The "kicker" comprises a lever at one side of the cup, pivoted at the side of the cup which extends to form part of the base of the cup. By pushing down or up on the lever the produce in the cup may be ejected from the cup. Disadvantages of this system are that depending upon the placement of the fruit within the cup, the action of the kicker can cause fruit to be catapulted from the cup rather than tipped as is the preferred method as well as the kicker resulting in bruising to the fruit. Also, it has been found that the shape of the member which comes in contact with the fruit has caused problems as if it is too small, the produce may be moved to either side of the member without being ejected from the cup. These devices have allowed ejection only to one side of the conveyor thereby limiting the overall performance of the grading system. With one sided ejection, in a case when fruit in consecutive carriers are destined for the same station, the chances are high that a collision could occur, bruising the fruit.
A further device comprises a variation to the mechanism of the previously mentioned back-ripping system where the produce is dropped to one side of the cup. This one sided limitation as has been previously mentioned reduces the overall performance of the system as only one side of the conveyor chain is being utilised to, for example, accept fruit for packaging.
The accuracy of weight measurements in many prior art cups has also been of concern. While it is possible to have a video camera image of a piece of fruit used to estimate the weight of substantially round produce, irregular shaped produce must be rotated to obtain more shape information. Other systems use load cells with an arrangement whereby the cups are passed over the sensor to cause a voltage impulse waveform, indicative of the weight of the fruit, to be output by the load cell. In order to accurately determine the weight of the fruit it is necessary to allow sufficient time to pass between adjacent cups so that the individual impulses are recognisable and that the cup mechanism is capable of allowing the fruit to be weighed without the added effects of the conveyor belt system. These added effects include vibration from the system operation and the weight of the cup and conveyor system being mistakenly combined with the fruit weight.
Some prior art conveyor systems require a length of rollers to be fitted at the beginning of the chain to be used as a "singulator" whereby a process is undertaken which attempts to ensure that only one piece of fruit is placed in each grading cup, An example is disclosed in U.S. Pat. No. 3,627,117 to Whiteford. This process may set a slow speed for the system in addition to requiring that the number of cups and the length of the conveyor system be extended.